Control valves are commonly used in systems to control the flow of a fluid (e.g., a gas, a liquid, etc.) or any other substance through pipes and/or vessels to which they are connected. A control valve is typically composed of one or more inlets and outlets, and includes a flow control element or member (e.g., a valve gate, a piston, a valve plug, a closure member, etc.) that operates to control fluid flow through apertures that fluidly couple the inlet(s) to the outlet(s). A flow control member is typically coupled to a valve bonnet assembly that is mechanically coupled (e.g., bolted, clamped, threaded into, etc.) to the valve body. Typically, the flow control member is configured to engage a sealing structure (e.g., a seat ring) that encompasses a flow path through the valve.
An actuator is typically coupled to the valve bonnet and includes an actuator stem that engages a valve stem to produce a torque and/or a thrust on the flow control member to control fluid flow through the valve. Actuators often include one or more springs that apply a biasing force to the actuator stem to move the flow control member to, for example, an open or closed condition in the absence of a control signal. The loading force provided by the spring(s) determines the position of the actuator stem and, thus, the position of any flow control member operatively coupled thereto for a given control signal. Additionally, for a given input or control signal, the spring load is set to achieve a target valve seat load when the valve is in a closed position and a target valve back seat load when the valve is in an open position.
When the valve actuator is manufactured, the spring(s) may be selected based on theoretical spring performance. However, due to manufacturing tolerances relating to springs and/or spring housing components, actual spring performance often deviates from theoretical spring performance, which may result in valve seat loads that are too low or too high. Insufficient or excessive valve seat loads can lead to improper valve operation. Depending on the deviation from the theoretical spring performance, the spring load can be increased or decreased in an attempt to achieve the target valve seat load and the target valve back seat load.
In some known actuators, to adjust for the discrepancy between the actual spring performance and the desired target or theoretical spring performance, it is necessary to disassemble the actuator to adjust the spring load by either adding or removing shims and/or spacers and then reassembling the actuator. After the actuator is reassembled, the actuator can be retested to determine if the actual spring performance provides the desired target valve seat load and the target valve back seat load. If not, the laborious process of disassembling the actuator to adjust the spring load must be repeated. Further, because shims and/or spacers are typically manufactured in specialized assembly shops in an other location from where the actuators are assembled and tested and an other location from where the actuators are installed, the customers or other users may not have the proper resources (e.g., proper tools, trained employees, etc.) to manufacture the shims and/or spacers to properly adjust the spring load.